[lmi] Segfault with updated wx

[Greg Chicares]

We're trying to create a reproducible test case, but I thought
it would be better to share this JIT debugger output right away.
Both Kim and I have encountered this segfault today with a
recently-updated wx build (which also enables threads: commit
0502765e2a6389edb7a1232f32a9e4c9102a429e). We've never seen
this problem with earlier wx versions.

lmi_wx_shared.exe caused an Access Violation at location 62ca834c in module 
wxmsw311u_gcc_gcc-491-97e6a75d1a83e5597942741f8382c3d4.dll Reading from 
location 00000000.

Registers:
eax=047c2728 ebx=0621f310 ecx=00000000 edx=00000000 esi=047c2728 edi=00000000
eip=62ca834c esp=0022f5e0 ebp=0022f648 iopl=0         nv up ei pl nz na po nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=00000206

Call stack:
AddrPC     AddrReturn AddrFrame  AddrStack  Params
62CA834C   62CA98D8   0022F648   0022F5E0   00000000   00000000   047C2728   
62CAF03E
62CA834C  
wxmsw311u_gcc_gcc-491-97e6a75d1a83e5597942741f8382c3d4.dll:62CA834CC:\opt\lmi\local\lib\wxmsw311u_gcc_gcc-491-97e6a75d1a83e5597942741f8382c3d4.dll:
 No symbol found
  _ZNK6wxGrid23GetDefaultEditorForCellEii
DEBUG_EVENT:
        dwDebugEventCode = EXIT_THREAD_DEBUG_EVENT
        dwProcessId = 564
        dwThreadId = 348
        dwExitCode = 0
DEBUG_EVENT:
        dwDebugEventCode = EXIT_THREAD_DEBUG_EVENT
        dwProcessId = 564
        dwThreadId = 4F8
        dwExitCode = C0000005
DEBUG_EVENT:
        dwDebugEventCode = EXIT_PROCESS_DEBUG_EVENT
        dwProcessId = 564
        dwThreadId = 78
        dwExitCode = C0000005